1. Field of the Invention
The invention relates to a heat dissipating device, and more particularly to a heat dissipating fan using a single high-efficiency motor to drive a plurality of rotors.
2. Description of the Related Art
With rapid development of electrical industry, natural convection is gradually being replaced by fans to dissipate the generated heat from electronic devices. Motors supply power to the fans for generating a large volume of airflow to dissipate a lot of heat from electronic elements. The way of increasing the volume of airflow is to increase the rotational speed of the fan, but the rotational speed of the fan cannot be arbitrarily increased. When the impeller of the fan rotates at high speed, the blades of the impeller bear large pressure and the loads on the motor and bearings thereof also increase. Accordingly, the blades of the impeller are easily deformed or even broken, and life of the fan is also shortened.
Serial arrangement of the fans is an alternative method of solving the described problem. Serially arranged fans rotate at a low speed but achieve the equivalent efficiency to a single fan rotated at a high speed. In FIG. 1, three fans 1, 1′ and 1″ are serially arranged. The fan 1 is independently actuated by a motor 11, the fan 1′ is independently actuated by a motor 11′, and the fan 1″ is independently actuated by a motor 11″.
When the number of serially arranged fans increases, particularly in small electronic devices, the volume, cost and difficulties in deploying the fans and the corresponding motors also increase. Moreover, when the impeller is rotated at high speed, the blades bearing high pressure are easily deformed or even broken.